GROUP 2 Flashcards
Describe the trend in atomic radius in group 2
Increases down the group
More shells of electrons
Bigger atom
Describe the trend in melting point of group 2
Decreases down the group
Metallic binding weakens
As atomic size increases
Distance between positive ions and delocalised ions increases
Electrostatic forces weaken
Describe the trend in 1st ionisation energy of group 2
Increases down group
Outermost electrons held more weakly
Further from nucleus
Outer shell more shielded
Describe the trend in reactivity in group 2
Increases down the group
How do the group 2 elements react with oxygen
Burn
Mg burns a bright white flame (MgO white solid with high melting point due to ionic bonding)
How does Mg react with oxygen without a flame
Magnesium oxide forms on the outside of Mg ribbons
Must be cleaned by emery paper
Gives false result
Because Mg and MgO react at different rates
How do the group 2 elements react with cold water
Form hydroxides and hydrogen
X(OH)2 (aq) + H2
How does magnesium react with steam and warm water
Burns in steam to produce MgO and hydrogen (bright white flame)
Slower reaction in warm water
Produces magnesium hydroxide and hydrogen
Outline the observations made when group two elements react with water
Fizzing (more vigorous down group)
Metal dissolving (faster down group)
Solution heating up (more down group)
CALCIUM ONLY: White precipitate forms
Why is titanium a useful metal?
Abundant
Low density
Corrosion resistant
Used to make strong light alloys
Why can’t titanium be extracted with carbon or electrolysis
TiC (titanium carbide) forms rather than titanium
Titanium has to be very pure
Outline the steps in which titanium is extracted
TiO2 + 2Cl2 > TiCl4 + 2CO (at 900C)
TiCl4 is purified by fractional distillation in Ar atmosphere
TiCl4 + 2Mg > Ti + 2MgCl2 (Ar atmosphere at 500C)
Why is titanium expensive
Mg is expensive
Batch processes (slower process requiring more labour and energy lost when reactor is cooked)
Argon atmosphere and need for moisture removal
High temperatures
Describe the trend in solubility in down group 2 hydroxides
Increases down the group
Appear as white precipitates when insoluble
Describe the state of magnesium hydroxide in water
Insoluble
Slightly alkaline so hydroxide ions must be produced
Outline the simplest ionic equation for the formation of Mg(OH)2 (s)
Mg2+ (aq) + 2OH- (aq) > Mg(OH)2 (s)
How is magnesium hydroxide used in industry
Medicine to neutralise excess acid in the stomach and treat constipation
Mg(OH)2 + 2HCl > MgCl2 + 2H2O
Safe due to weak alkaline state
Describe the reaction of calcium hydroxide with water
Reasonably soluble
Outline the uses of calcium hydroxide in industry
Neutralise acidic soil
Test for CO2
Limewater turns clear to cloudy
Due to CaCO3 production
Describe the solubility of barium hydroxide
Easily dissolves
Strongly alkaline
Describe the trend in solubility of group 2 sulphates
Decreases down the group (less soluble)
BaSO4 least soluble
Outline the full and ionic equations for the formation of the precipitate with group 2 sulphates
SrCl2(aq) + Na2SO4(aq) > 2NaCl(aq) + SrSO4(s)
Sr2+(aq) + SO4^2-(aq) > SrSO4(s)
Outline the use of BaSO4 in industry
Absorbs x-Rays
To show up the gut on an x-Ray image
safe due to low solubility
How does barium metal react with sulphuric acid
Slowly
Insoluble barium sulphate produces covers the surface if metal to act as a barrier to further attack
Ba + H2SO4 > BaSO4 + H2
How is BaCl2 solution acidified with hydrochloride acid used as a reagent to test for sulphate ions
Ba2+(aq) + SO4^2-(aq) > BaSO4(s)
Barium sulphate is a white precipitate
Other anions give a negative result
Why is hydrochloric acid used to test for the presence of a sulphate ion
To react with carbonate impurities found in salts
That would frozen barium carbonate a white participate
That gives a false result
How can insoluble salts be formed?
Mixing appropriate ion solutions so a precipitate is formed
What is a spectator ion
An ion not changing state
And not chasing oxidisation number
What are the steps to writing an ionic equations for a precipitation reaction
Full equation
Ba(NO3)2(aq) + Na2SO4(aq) > BaSO4(s) + 2NaNO3(aq)
Separate (aq) solutions into ions
Ba2+ + 2NO3- + 2Na+ + SO4^2- > BaSO4 + 2Na+ + 2NO3-
Cancel out spectator ions
Ba2+ + SO4^2+ > BaSO4
